The present disclosure relates to a thin film transistor, and a method of manufacturing the thin film transistor.
Thin film transistor (TFT) is often used in a liquid crystal display panel as an active element for driving a pixel electrode for displaying pixels. TFTs include TFTs using an amorphous silicon as a semiconductor material and TFTs using a polycrystalline silicon as a semiconductor material. The mobility in a polycrystalline silicon is higher than in an amorphous silicon. Therefore, the TFT formed using a polycrystalline silicon can operate faster. On the contrary, since the mobility in an amorphous silicon is lower than in a polycrystalline silicon, the TFT formed using an amorphous silicon can reduce off-state leakage current.
JP 2012-114131 A discloses a TFT using properties of both of an amorphous silicon and a polycrystalline silicon. This TFT includes a gate electrode formed on an insulating substrate; an insulating layer formed to cover the substrate and the gate electrode; a polycrystalline silicon layer formed on the insulating layer; an amorphous silicon layer formed on the polycrystalline silicon layer; and a source electrode and a drain electrode formed on the amorphous silicon layer. The polycrystalline silicon layer is formed by forming an amorphous silicon layer and then treating the amorphous silicon layer with laser radiation to convert the amorphous silicon into the polycrystalline silicon. The polycrystalline silicon layer and the amorphous silicon layer serve as a channel layer. The TFT has an intermediate property such as mobility between the property of the channel layer formed by polycrystalline silicon layer and the property of the channel layer formed by amorphous silicon layer.
Further, there are technologies being developed in which a part of the amorphous silicon layer is converted into the polycrystalline silicon by treating a part of the amorphous silicon layer with laser radiation, instead of converting the entire amorphous silicon layer into a polycrystalline silicon. Properties of a TFT can be properly adjusted by controlling an amount of the amorphous silicon to be converted into the polycrystalline silicon layer.